Adhesives and adhesive tapes



United States Patent 3,441,430 ADHESIVES AND ADHESIVE TAPES Richard L.Peterson, Hudson, Wis., assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn., a corporation of Delaware No Drawing. FiledNov. 19, 1964, Ser. No. 412,329 Int. Cl. C09d 3/66; C09j 7/02; C08c17/16 US. Cl. 117-685 Claims ABSTRACT OF THE DISCLOSURE Repulpablesplicing tapes which adhere to wet or hydrophilic surfaces are made bycoating one or both surfaces of a paper backing with a water-solublecopolymer of an acrylic acid and an ether acrylate, plasticized with atleast an equal amount of a liquid Water-soluble plasticizer having atleast one ether linkage, e.g., polyethylene glycol monophenyl ether.

This invention relates to water soluble aggressively tacky adhesives andto tacky adhesive tapes made therewith. An especially preferredembodiment of this invention is a repulpable adhesive tape which findsparticular utility in splicing rolls of papers.

Paper making and printing operations require splicing the end of oneroll of paper to the beginning of another, as Well as splicing togethera roll after defective material is cut out. It is important that suchsplices be made quickly and easily, necessitating the use of an adhesivewhich rapidly attains maximum strength and which retains that strengththroughout subsequent operation. So that the spliced areas, which areeventually cutout, can be returned to the paper mill for reprocessing,it is extremely desirable that the splice, including the adhesive whichis used to make it, be repulpable. This combination of requirementsprecludes the use of conventional normally tacky and pressure-sensitiverubber-resin adhesives.

The most popular paper-splicing tape prior to the present invention isdescribed and claimed in Sohl US. Patent 2,838,421, where adhesives aremade from polyvinylcarboxylic acids such as polyacrylic acid blendedwith a permanent plasticizer such as polyethylene glycol orpolypropylene glycol. Double-coated paper tapes made with theseadhesives are widely used in the paper making and printing industrytoday; although excellent in many respects, splices made with suchadhesives show a tendency to bleed through succeeding laps of paper atconditions of high humidity or temperature. When this occurs, adjoiningconvolutions may become so tightly adhered together that the paperactually tears during processing. Attempts have been made to reducebleeding by modifying the Sohl adhesive, e.g., by copolymerizing a loweralkyl acrylate with acrylic acid, but such adhesives have been foundextremely difficult to repulp under typical field conditions. Someeiforts have also been made to replace polyacrylic acid with such otherwater-soluble adhesives as polyvinylpyrrolidone, but these attempts haveresulted in products which are inferior in both bleed-resistance andheat-resistance.

Like the Sohl adhesive, the present invention provides an elastic,rubbery product which adheres tenaciously to hydrophilic surfaces suchas paper, even when those surfaces are wet. This invention alsoprovides-for the first time, insofar as applicant is aware-a productwhich essentially eliminates the problems of Waste paper and breakagecaused by adhesive bleeding. The adhesive of this invention has highinternal strength, maintaining that strength even at the elevatedtemperatures often attained in the curing of printing inks. Equallysignificantly, this adhesive and splicing tapes made therewith retainthe es- 3,441,430 Patented Apr. 29, 1969 sential quality ofrepulpability under conventional paper making conditions.

The invention includes a water-soluble humidityand heat-resistantpolymer made by copolymerizing 60 to parts by weight of an 0: 3unsaturated monocarboxylic acid (especially acrylic or methacrylic acid)and correspondingly from 40 to 5 parts by weight of a water-solublehomopolymerizable alkoxy alkyl ester of such an acid (e.g., methoxyethyl, methoxy butyl or 2-ethoxyethyl acrylate, or polyoxyalkyleneglycol ether acrylates). The finished copolymer, in 15% solids solution,has a Brookfield viscosity at 80 F. in the range of 5,000 to 100,000cps. The adhesive composition also includes from to 200 parts by weight(based on 100 parts by weight of copolymer) of a compatible liquidwater-soluble plasticizer having at least one ether linkage and anaverage molecular weight in excess of about 200; suitable materialsinclude polypropylene glycol, polyethylene glycol, or, preferably,polyethylene glycol monophenyl ether. In order to provide improved heatresistance, the adhesive composition also preferably includes from about/2 to about 3 parts per 100 parts of copolymer of a polyfunctionalcrosslinker, e.g., water-soluble polyfunctional amines such astriethylene tetramine, diethylene triamine, or, preferably hexamethylenediamine. The adhesive composition may also contain up to about 2 partsper 100 parts of copolymer of the hydroxide of a monovalent cation,e.g., sodium hydroxide, potassium hydroxide, or ammonium hydroxide. Anaggressively tacky paper-adherent tape product is made by coating one orboth sides of a sheet backing, especially a tissue paper backing, with asolution of this adhesive and evaporating the solvent.

The following examples are provided, not by way of limitation, butmerely as illustration of presently preferred embodiments of thisinvention.

EXAMPLE 1 2:1 water:acetone solution containing 12% acrylic acid and 3%ethoxyethyl acrylate is copolymerized in a glasslined kettle, employingpotassium persulfate as a catalyst and mercapto acetic acid as a chaintransfer agent, so as to obtain a product solution containing about 15%solids and having a Brookfield viscosity in the range of 5,000 to100,000 cps. at 80 F. Approximately 22.5 parts by weight of polyethyleneglycol monophenyl ether having an average molecular weight of 270(available commercially, as Pycal 94, from the Atlas Powder Company) isthen added at room temperature, while the copolymer solution isconstantly stirred. To the composition is then slowly addedapproximately 0.25 part by weight of hexamethylene diamine (as a 70%solution in water) and approximately 0.25 part of NaOH; these alkalinematerials neutralize sulphuric acid formed during the decomposition ofthe potassium persulfate catalyst; the diamine also serves as aneffective crosslinker to impart strength to the adhesive used at hightemperatures. If desired, a dye such as malachite green may be includedin the composition in order to color the adhesive and make coatingsthereof more readily visible. Total adhesive solids of this compositionconstitutes about 30% by weight of the solution. The adhesivecomposition can either be used per se or coated on a sheet backingmaterial in conventional manner to form a tacky adhesive tape.

EXAMPLE 2 To one surface of a paper liner, coated on both sides with asilicone release agent, was applied approximately 8%. dry grains per 24square inches, of the adhesive of Example 1, and the solvent evaporatedby heating in a forced air oven for approximately 2% minutes at 200 F.An open wood fiber tissue paper having a basis weight 3 of 8 pounds perpapermakers ream was then laminated to the dried tacky adhesive bypassing the adhesive-coated liner and the tissue paper web through a setof squeeze rolls. The exposed paper surface of the laminate was thencoated with approximately the same amount of adhesive, the solvent againevaporated, and the composite double-coated laminate wound on itself inroll form. The

no localized areas where color change occurs, further substantiating thetotal repulpability of the splice.

The following examples, presented in tabular form, illustrate repulpableadhesive systems which may be made in accordance with the presentinvention, indicating the effect of various changes in composition onthe finished product.

Copolymer Parts per 100 parts of copolymer Alkoxy Acidzester Chain alkylmonomer Diamine transfer Ex. Acid ester ratio Plasticizcr Plasticizercrosslinker agent Alkali Comments 3 Acrylic 2-ethoxy 95:5 Polyethylene150 2.2 0.02 1.6 More hygroscopic than Exethyl glycol monoample 1;suitable for high acrylatc. phenylether. caliper open papers; ex-

cellent at elevated temperatures.

150 2. 2 0.01 1. 1 General purpose; excellent at both room and elevatedtemperatures.

150 0. 9 0. 05 O. 4 Similar to 4 but more hydroscopic.

150 0. 9 0.01 0. 4 Similar to 1, but slightly more flexible at hightemperatures.

150 0. 0 0.01 0. 4 Similar to 4.

100 1.7 0.01 0.7 Less hydroscopie than 1;

suitable for dense and/or coated papers; excellent at room temperature.

8 methacryllc do 00:10 .do 200 0.5 0.01 General purpose; lesshydroscopic than comparable adhiesive made with acrylic 301 monomer.

9 Acrylic Methoxy 80:20 -do 200 2. 2 0.03 1. 6 General purpose; lesshydrobutyl scopie and more flexible acrylate than 1. 10 ..do 2-ethoxy80:20 Polyethylene 200 0. 0 0.03 0.7 Outstanding splice strength ethylglycol, ave. but less tack and greater acrylate MW=1,000. tendency tobleed than 1. 11 ..do ..do 80:20 Polypropylene 200 0. 0 0. 03 0. 7Similar to 10.

glycol, ave. MW=425.

tape product of this example functions especially effectively in thepreparation of splices in paper making and printing operations. Evenafter being subjected to temperatures of 400 F. the entire spliceconstruction can be readily repulped in conventional equipment usingconventional deinking and paper making chemicals and procedures.

When two strips 1% inch unbleached 40 lb. kraft paper were joined with a1 inch x 1% inch strip of the tape just described, it was found that theshear strength of the splice exceeded the tensile strength of the paper.When an identically made splice was subjected to a constant shearingforce of 1 kilogram, the splice lasted approximately 7 times as longbefore failure as a splice made with the best previously knownrepulpable splicing tape. When splices were similarly evaluated at 400F., it was found that splices made with the tape of the example lastednearly 4 times as long before failure as splices made with the 'bestpreviously known splicing tape.

When paper spliced with the tape product of this example is woundtightly into a roll, no noticeable bleeding of the adhesive to adjacentlayers is detected, and the roll can be easily unwound even afterseveral days exposure to high humidity. The adhesive remains tacky andshows no tendency toward pastiness. When the best previously availabletape product is similarly employed, high humidity causes bleeding toadjacent layers, especially with light weight or open papers. Thisbleeding not only causes waste of soiled paper; it also tends to bondadjacent laps of paper tightly together, often resulting in breakage andresultant down time when the roll is unwound.

Even after being subjected to temperatures of 200- 400 F., splices madein accordance with this example can readily be repulped, usingconventional equipment, chemicals, and paper making techniques. Papersheets made from stock containing such repulped splices display noagglomerates of adhesive or splice material when examined under themicroscope. When the repulped furnish is checked by adding methyl redsolution, there are As previously indicated, those skilled in the artwill be able to effect numerous changes in the practice of thisinvention. For example, as is well known, polymerization may beinitiated by ultraviolet light, heat, a peroxide, instead of thepotassium persulfate catalyst named. Likewise, conventional chainmodifiers (or chain transfer agents) of the thiol, thio-organic acid, orsimilar families may be employed; generally speaking, as is well-known,the more of such agent added, the lower the average molecular weight ofthe product. Again, speaking in general terms, the lower the averagemolecular weight, the more fluent the product and the greater thenecessity for employing a crosslinking agent. Products havingappreciably less than about /z% crosslinking agent based on thecopolymer generally tend to be unsatisfactory for applications wherespices are subjected to high heat, as is common in the printingindustry. Likewise, when the crosslinking agent is present in excess ofabout 3% water solubility of the adhesive is decreased, and splices tendto be insufiiciently repulpable and/ or insufliciently tacky,particularly after exposure to high temperature.

Although the monophenyl ether of polyethylene glycol has proved to beespecially satisfactory as a plasticizer for adhesives made inaccordance with this invention, other compatible liquid water solubleplasticizers having at least one ether linkage and a molecular weightabove about 200 may also be successfully employed. If the molecularweight of the plasticizer falls below about 200 (e.g., if diethyleneglycol is employed), the adhesive tends to be too fluent, and excessivebleeding of splices occurs; this problem may be obviated either by theinclusion in the molecule of aromatic groups or employing a highermolecular weight, e.g., tetraethylene glycol or higher polyethers. Theplasticizer is added in that amount which is suflicient to improve tackwhile maintaining adequate strength and bleed resistance. Generallyspeaking, lower molecular weight copolymers, or those having relativelyhigher amounts of alkoxy alkylester comonomer, may employ as little asparts of plasticizer per 100 parts of copolymer; higher molecular weightcopolymers, or those employing a less soluble acid comonomer, may

require as much as 200 parts of plasticizer per 100 parts of copolymer.It has been found that 150 parts of plasticizer per 100 parts ofcopolymer is satisfactory in almost all cases. Specific changes,however, may be made to adapt to specific conditions. For example, whereextremely dense or dry paper is being spliced or where the humidity ofthe plant is extremely low, it may be desirable to increase the amountof plasticizer normally used.

Where acrylic or methacrylic acid is employed as the dominant comonomer,the other comonomer employed should itself be water soluble; if thisprecaution is not observed, the finished adhesive product itself islikely to be extremely difiicult, if not impossible, to repulp. Thehigher the molecular weight of the ether ester monomer, the lower thequantity which should be employed to produce a satisfactory copolymer,but an increase in the number of ether linkages in the molecule tends tooffset even this generalization. If less than 5% of the ether estercomonomer is employed, the water sensitivity and bleeding tendency ofthe finished adhesive is almost certainly too high; likewise, if over40% of the ether ester comonomer is employed, the adhesive is mainlysuitable for only extremely dense papers and is extremely difiicult torepulp.

Although this invention has been particularly described with respect toa splicing tape for paper making and printing operations, it has beenpointed outthat the adhesive per se has other uses. Water-solubleadhesive labels may be applied to dishes, windows, or other surfaceswhich it is common to clean with aqueous sol-vents. Cloth garment labelscoated with this adhevise may readily be washed from the garments towhich they are affixed. Likewise, since the adhesive is substantiallyinsoluble in most oils or similar hydrocarbon solvents, it may beemployed in applications where conventional normally tacky andpressure-sensitive adhesive tapes prove unsatisfactory.

What I claim is:

1. An adhesive tape having on at least one face a layer of normallytacky, water-soluble, aggressively paperadherent, humidity-resistantheat-resistant adhesive which consists essentially of 100 parts byweight of a copolymer formed from 60 to 95 parts by weight of acrylic ormethacrylic acid monomer and correspondingly from 40 to 5 parts byweight of the water-soluble ether ester of such an acid, and 100 to 200parts of compatible liquid water-soluble plasticizer having at least oneether linkage and a molecular weight above about 200.

2. An article according to claim 1 wherein the a-[S unsaturated acidmonomer is acrylic acid.

3. An article according to claim 1 wherein the ap unsaturated acidmonomer is methacrylic acid.

4. An article according to claim 1 wherein the ether ester is2-ethoxyethyl acrylate.

5. An article according to claim 1 wherein the ether ester ismethoxybutyl acrylate.

6. An article according to claim 1 wherein the copolymer is formed fromabout parts of acrylic acid and about 20 parts of 2-ethoxyethylacrylate.

7. An article according to claim 1 wherein the plastizer is polyethyleneglycol monophenyl ether.

8. An article according to claim 1, further characterized by theinclusion of /2 to 3 parts of polyfunctional crosslinking agent.

9. A repulpable bleed-resistant tape especially suitable for splicingrolls of paper, comprising a tissue paper sheet provided on both faceswith a layer of normally tacky, water-soluble, humidity-resistant,heat-resistant adhesive, said adhesive consisting essentially of thedried reaction product of 100 parts water-soluble copolymer formed from5 to 40 parts by weight of ether acrylate monomer and correspondinglyfrom to 60 parts acrylic acid monomer, said copolymer in 15% aqueoussolution at 80 F. having a Brookfield viscosity in the range of 5,000-100,000 centipoises, to 200 parts of polyethylene glycol monophenylether, 0' to 2 parts of monovalent cation hydroxide, and /2 to 3 partsof polyfunctional crosslinking agent.

10. An article according to claim 9 wherein the crosslinking agent is awater-soluble polyamine.

References Cited UNITED STATES PATENTS 2,838,421 6/1958 Sohl 117-685 X2,884,126 4/1959 Ulrich 206-59 2,945,013 7/1960 Ott 260-861 2,973,2862/1961 Ulrich 117-122 3,096,202 7/1963 De Groot Von Arx 117-6853,098,760 7/1963 Ericks 117-143 3,307,544 3/1967 Gander et a1 128-156WILLIAM D. MARTIN, Primary Examiner.

B. PIANALTO, Assistant Examiner.

US. Cl. X.R.

